A Roth in-plan conversion is an accounting move that shifts pre-tax dollars sitting in your 401(k), 403(b), or governmental 457(b) into the designated Roth account within that same plan.1Internal Revenue Service. Roth Account in Your Retirement Plan The money never leaves the plan and your investments don’t change; what changes is the tax label. You pay ordinary income tax on the converted amount for the year of the transfer, and in exchange the money grows tax-free and comes out tax-free in retirement, provided you meet the rules below.
How the Mechanic Works
Picture your employer plan as two buckets. The traditional bucket holds contributions that reduced your taxable income when you made them, plus their earnings. The Roth bucket holds after-tax money that will eventually come out tax-free. A conversion moves dollars from the first bucket to the second, all inside the same plan at the same recordkeeper.
No check is mailed to you. Nothing is rolled to an outside institution. The plan administrator records the transfer, adds the previously untaxed amount to your gross income for the year, and from that point forward those dollars follow Roth rules. Qualified withdrawals later are completely tax-free.1Internal Revenue Service. Roth Account in Your Retirement Plan
The statutory authority sits in Section 402A(c)(4) of the Internal Revenue Code, which treats the transfer of non-Roth plan money into a designated Roth account as a taxable rollover.2Office of the Law Revision Counsel. 26 U.S. Code 402A – Optional Treatment of Elective Deferrals as Roth Contributions This is different from a Roth IRA conversion, which moves the money out of the employer plan entirely and into a Roth IRA at a brokerage. Keeping everything inside the plan changes some of the mechanics, especially the five-year rule.
Does Your Plan Even Allow It
The IRS permits Roth in-plan conversions. Your employer decides whether to offer them. Two things have to be true.
First, the plan must include a designated Roth account, which is a separate account within the plan that tracks Roth contributions and their earnings apart from pre-tax money.3Internal Revenue Service. Retirement Topics – Designated Roth Account If there’s no Roth side of the plan, there’s nothing to convert into. Governmental 457(b) plans qualify alongside 401(k) and 403(b) plans if they include the Roth feature.4Internal Revenue Service. IRC 457(b) Deferred Compensation Plans
Second, the plan document has to permit the conversion itself. There are two paths a plan can take.
The narrower path only lets you convert money that is already distributable under the plan’s normal rules. That usually means reaching age 59½, separating from service, becoming permanently disabled, or death.5Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions If none of those apply, the conversion isn’t available under this path.
The broader path is what makes the strategy powerful for younger workers. Section 402A(c)(4)(E) allows plans to let you convert money that is not otherwise distributable.2Office of the Law Revision Counsel. 26 U.S. Code 402A – Optional Treatment of Elective Deferrals as Roth Contributions Under this feature, a 35-year-old still on payroll can convert without any triggering event. Many large plan sponsors have adopted it; not all have. Your plan administrator or summary plan description will tell you which version your plan uses.
What You Can Convert
Assuming the plan allows it, several types of money on the pre-tax side are eligible:
- Pre-tax elective deferrals you made from your paycheck.6Internal Revenue Service. 401(k) Plan Overview
- Investment earnings on those contributions.
- Employer matching and profit-sharing contributions, to the extent vested.
- Pre-tax rollover money you brought in from a prior employer’s plan or a traditional IRA.
- Voluntary after-tax (non-Roth) contributions, if your plan allows them. The after-tax portion isn’t taxed again; only the earnings on those contributions are taxable at conversion.
What You Pay in Tax
The entire pre-tax amount you convert counts as ordinary income for the year of the transaction. Convert $50,000 of pre-tax money and your taxable income for that year rises by $50,000, both federally and in states that tax retirement income.1Internal Revenue Service. Roth Account in Your Retirement Plan
The conversion itself does not trigger the 10% early withdrawal penalty, even if you’re under 59½. The statute specifically exempts the rollover from Section 72(t).2Office of the Law Revision Counsel. 26 U.S. Code 402A – Optional Treatment of Elective Deferrals as Roth Contributions But pay the resulting tax bill with money from outside the plan. If you take a separate distribution to cover the taxes and you’re under 59½, that withdrawal can be hit with the 10% penalty.7Internal Revenue Service. Topic No. 558, Additional Tax on Early Distributions from Retirement Plans Other Than IRAs Paying from outside also keeps every dollar of the converted amount compounding tax-free.
If the conversion pulls in after-tax contributions you previously made, those specific dollars aren’t taxed again since you already paid tax on them. Only pre-tax contributions and any earnings on the after-tax contributions show up as taxable income. The plan tracks the basis.
A large conversion can leave your paycheck withholding short of what you owe. To avoid an underpayment penalty, either raise your W-4 withholding for the rest of the year or make a quarterly estimated payment with Form 1040-ES.8Internal Revenue Service. Form 1040-ES – Estimated Tax for Individuals
How It Shows Up on Paper
Your plan administrator reports the conversion on Form 1099-R. The total converted amount goes in Box 1, the taxable portion in Box 2a, and any after-tax basis in Box 5. Box 7 carries distribution Code G, which the IRS uses for direct rollovers within qualified plans, including in-plan Roth rollovers.9Internal Revenue Service. 2025 Instructions for Forms 1099-R and 5498
You Cannot Undo It
Before 2018, a Roth conversion could be reversed through recharacterization. The Tax Cuts and Jobs Act eliminated that option for conversions completed in 2018 and later. Once you convert, the tax bill is locked in. If the market drops or your income turns out higher than you planned, there’s no rewind. That makes it worth modeling the tax impact before you file the paperwork.
The Five-Year Rule
Getting money out tax-free requires two conditions: you must be at least 59½, and at least five tax years must have passed since your first Roth contribution or in-plan Roth conversion to that plan.1Internal Revenue Service. Roth Account in Your Retirement Plan Meet both and the distribution is qualified: contributions and earnings come out completely tax-free.10Internal Revenue Service. Roth Comparison Chart
The clock starts on January 1 of the tax year of your first designated Roth contribution or in-plan Roth rollover to the plan.11Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts If you’ve been making Roth 401(k) contributions since 2020, that clock has already run. A conversion you do in 2026 does not restart it. Withdraw the taxable portion of a conversion before satisfying the five-year rule and while under 59½, and the 10% early withdrawal penalty can apply. Earnings withdrawn before you qualify are both taxable and potentially penalized.
How This Differs From a Roth IRA Conversion
The two conversions look similar but differ in ways that can drive the choice.
One Clock, Not Many
A designated Roth account uses a single five-year clock that starts with your first Roth contribution or conversion to that plan. Every later conversion benefits from that same clock. A Roth IRA conversion starts its own five-year waiting period for penalty-free access to the converted principal. If you plan a series of conversions, the in-plan route is simpler.11Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts
No Pro-Rata Headache
When you convert a traditional IRA to a Roth IRA, the IRS aggregates all your traditional IRA balances. If part is pre-tax and part is after-tax, each conversion is treated as coming proportionally from both. That is the pro-rata rule, and it often makes backdoor Roth IRA conversions partially taxable for people with large traditional IRA balances.
In-plan conversions don’t work that way. The plan tracks pre-tax and after-tax money in separate sources, so you can convert one source without triggering a proportional pull from unrelated accounts. IRS Notice 2014-54 confirmed that when distributing from a plan, pre-tax and after-tax amounts can be directed to different destinations.12Internal Revenue Service. Guidance on Allocation of After-Tax Amounts to Rollovers
No More Lifetime RMDs
Before 2024, designated Roth accounts in employer plans were subject to required minimum distributions during the account owner’s lifetime, unlike Roth IRAs. SECURE Act 2.0 eliminated lifetime RMDs for designated Roth accounts in 401(k) and 403(b) plans starting in 2024.13Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs Both types of Roth accounts are now free of lifetime RMDs. Beneficiaries who inherit either still face distribution requirements.14Internal Revenue Service. Retirement Topics – Required Minimum Distributions (RMDs)
When a Conversion Actually Pays Off
The central question is whether your tax rate now is lower than the rate you expect in retirement. A temporarily low-income year, such as time between jobs, an unpaid leave, or the gap between retiring and starting Social Security, is often the best conversion window. You lock in a lower rate on money that would otherwise be taxed at potentially higher rates later.
Time horizon matters too. A 35-year-old converting $20,000 captures decades of tax-free compounding. A 62-year-old converting three years before drawdown captures far less growth, though the math can still work if the money is destined for heirs, since inherited Roth distributions are tax-free (beneficiaries generally must empty the account within 10 years).15Internal Revenue Service. Retirement Topics – Beneficiary
Conversions are harder to justify during peak earning years in a top bracket. Paying 35% now to avoid 22% later destroys value. The same logic applies if the conversion pushes you into a higher bracket or phases out other tax benefits. Partial conversions across several years usually beat one large lump: you can fill up a lower bracket each year without spilling over.
Watch the Medicare Two-Year Lag
A conversion raises your modified adjusted gross income, and that can raise your Medicare Part B and Part D premiums through the Income-Related Monthly Adjustment Amount. Medicare uses your tax return from two years prior, so a conversion in 2024 hits your 2026 premiums.
For 2026, the standard Part B premium is $202.90 per month. If your MAGI on the 2024 return exceeds $109,000 filing single or $218,000 filing jointly, the surcharge starts. At the first tier the monthly premium jumps to $284.10, and at higher income levels it can reach $689.90 per month.16Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles For a couple where both spouses are on Medicare, the added annual cost can run into the thousands. Timing conversions before Medicare eligibility, or sizing them to stay below the thresholds, is often worth the effort.
The Mega Backdoor Roth
If your plan allows both voluntary after-tax contributions and in-plan Roth conversions, you can move far more into Roth status than the regular deferral limits suggest. The elective deferral limit for 2026 is $24,500, or $32,500 with the age-50 catch-up, or $35,750 for ages 60 through 63.17Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026 But the total that can go into a defined contribution plan from all sources combined, including employer money, is much higher: $72,000 for participants under 50 in 2026.
After maxing your regular pre-tax or Roth contributions, you make additional voluntary after-tax contributions up to the overall plan limit and then convert those dollars to the designated Roth account. Because you already paid tax on the contributions, only the earnings, usually minimal if you convert quickly, are taxable. The result is tens of thousands of extra dollars per year in Roth status.
Every piece has to be in place: after-tax contributions allowed, in-plan Roth conversions allowed, and ideally frequent or automatic conversions so earnings don’t accumulate. Not every plan offers the combination. If yours does, it’s one of the more effective tax-planning tools available to a W-2 employee.